The objectives are to: a) identify the types and functions of mononuclear cell infiltrating the tumor mass at different stages of growth, i.e., from the time of tumor take through rapid growth and spontaneous regression; b) characterize the mechanism responsible for spontaneous regression of the tumor; and c) determine the mechanism of materno-offspring transfer of tumor immunity. The approach is to isolate the infiltrating mononuclear cells and identify their cell types and immunologic functions in vitro and in vivo.